Development apparatus for electrophotographic printing machine

ABSTRACT

An apparatus in which toner particles are deposited on an image bearing member having an electrostatic latent image recorded thereon for producing a viewable powder image thereof. Carrier granules flow from a storage region to a discharge region and are intermingled thereat with toner particles. The resulting mix of carrier granules and toner particles is directed to cascade over the image bearing member creating a toner powder image on the electrostatic latent image recorded thereon.

United States Patent Eto June 10, 1975 [54] DEVELOPMENT APPARATUS FOR 3.41 1,931 11/1968 gzrnsdet a1...| 118/636 RI [N 3.59 .604 8/1971 aw a eta. 18/637 f a ig ig P NT G 3,707,390 12/1972 Sullivan. Jr. 118/637 X 3,707,947 1/1973 Reichart. Jr. 118/637 [75] Inventor: YOShiO Eto. Omiya, Japan 3.724.422 4/1973 Latone et a1 1 18/637 3.823.689 7 1974 D' t2 118 637 [73] Assignee: Rank Xerox, Limited, London. c I

England Primary Examiner-Ronald Feldbaum [22] Filed: Jan. 30, 1974 Attorney, Agent, or Firm-H. Fleischer; J. J. Ralabate; [21 Appl. No.: 438,125 Green Related US. Application Data 57 ABSTRACT [62] g g 'ggg f Sept 1972* An apparatus in which toner particles are deposited on an image bearing member having an electrostatic latent image recorded thereon for producing a view- 355/3 86 able powder image thereof. Carrier granules flow from [58 i 24. a storage region to a discharge region and are intere 0 H7/l7 5 mingled thereat with toner particles. The resulting mix of carrier granules and toner particles is directed to cascade over the image bearing member creating a [56] References Cited toner powder image on the electrostatic latent image UNITED STATES PATENTS recorded thereon 3,367,306 2/1968 Lawes et a1 1 18/637 3,375,807 4/1968 Eichorn 118/637 4 Clam, 5 Drawmg figures PATENTEDJUH 10 1915 3,888,578

SHEET 3 DEVELOPMENT APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING MACHINE This is a division of application Ser. No. 290,!95, filed Sept. 18. I972, now US. Pat. No. 3,835,8I I.

The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as to the scope of the invention in any way.

BACKGROUND OF THE INVENTION This invention relates generally to electrostatographic printing, and more particularly concerns an apparatus for developing an electrostatic latent image recorded on an image bearing member.

In the process of electrostatographic printing, an image bearing member is charged to a substantially uniform level, and, thereafter, selectively discharged to form an electrostatic latent image thereon corresponding to an original document to be reproduced. The electrostatic latent image is developed, i.e. rendered visible, by depositing toner particles thereon. This visible toner powder image is fused to the image bearing member, or, in lieu thereof, transferred to a separate support sheet and fused thereto.

Electrostatographic printing includes electrographic printing and electrophotographic printing. These processes are quite similar to one another, in that, they both record an electrostatic latent image on an image bearing member. However, electrophotographic printing forms the latent image by irradiating a photoconductive surface, whereas electrographic printing does not require a photoconductive surface. The present invention is depicted as being used in a suitable electrophotographic printing machine, such as disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942. As described therein, a charged photoconductive surface is exposed to a light-image of the original document. The light-image irradiates the photoconductive surface to selectively dissipate the charge and record thereon the electrostatic latent image. A developer mix is brought into contact with the latent image to produce a powder image thereon. Typical developer mixes comprise dyed or colored thermoplastic particles, known in the art as toner particles, which are mixed with coarser carrier granules, such as ferromagnetic granules. The toner particles are triboelectrically attracted to the carrier granules and adhere thereto. However, as the developer mix contacts the latent image, the greater attractive force of the latent image causes the toner particles to transfer from the carrier granules to the latent image.

Numerous types of development systems are suitable for rendering the electrostatic latent image visible. For example, electrophotographic printing machines may utilize cascade development systems, magnetic brush development systems, powder cloud development systems, or liquid development systems. Presently, cascade development is the most common system used in typical commercial printing machines. In cascade development, the developer mix is transported from a sump or lower region to an upper region where it is discharged into a hopper to cascade in a downwardly direction over the photoconductive surface forming a toner powder image on the electrostatic latent image recorded thereon. Cascade systems include conveyor system arranged to advance the developer mix from the sump to the discharge region. Typical conveyor systerns employ buckets secured to an endless belt entrained about a pair of spaced rollers. The buckets pass through the sump and are filled with the developer mix which is transported in an upwardly direction therefrom to the hopper. At the hopper, the buckets discharge the mix enabling it to cascade in a downwardly direction over the photoconductive surface developing the latent image. Bucket conveyor systems are frequently large and unsuitable for small size electrophotographic printing machines.

As the developer mix cascades over the photoconductive surface, toner particles are attracted from the carrier granules to the electrostatic latent image. In this manner, the developer mix gradually becomes deplete of toner particles. Generally a toner dispenser is provided for adding additional toner particles, as required, to the developer mix. This maintains sufficient toner particles within the developer mix to provide adequate development of the latent image. However, in order to insure that the toner particles are triboelectrically attracted to the carrier granules, the toner particles must be mixed therewith. Conventional systems often utilize stirrers or other means for homogeneously mixing the toner particles with the carrier granules. This, too, in creases the size and complexity of the development apparatus.

It is, therefore, the primary object of the present invention to improve the development apparatus of an electrostatographic printing machine.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus for depositing toner particles on an electrostatic latent image recorded on an image bearing member.

This is accomplished, in the present invention, by means adapted to form a flow of carrier granules moving from a storage region to a discharge region. At the discharge region, means are provided for dispensing toner particles into the flow of carrier granules. Thereafter, means intermingle the carrier granules with the toner particles to produce a substantially uniform mix. Further in accordance with the present invention, the mix is directed to cascade over the electrostatic image creating a toner powder image thereon. Thus, in the particular device illustrated, carrier granules are intermingled with toner particles to establish a substantially uniform mix which cascades over the electrostatic latent image recorded on the image bearing member. In this manner, toner particles are deposited on the latent image producing a visible powder pattern in image configuration.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. I is a schematic perspective view of an electrophotographic printing machine embodying the features of the present invention therein;

FIG. 2 is an enlarged, sectional, elevational view of adevelopment apparatus utilized in the FIG. I printing machine;

FIG. 3 is an enlarged. fragmentary. perspective view of the FIG. 2 development apparatus;

FIG. 4 is an enlarged, fragmentary, perspective view of the guide member used in the FIG. 2 development apparatus; and

FIG. 5 is an enlarged, fragmentary, perspective view of a toner dispensing mechanism incorporated in the FIG. 2 development apparatus.

While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, wherein like reference numerals have been used throughout to indicate like elements, FIG. 1 illustrates an electrophotographic printing machine for producing a copy of an original document. The printing machine depicted in FIG. 1 includes a rotatably mounted drum having photoconductive surface 12 thereon. Drum 10 is rotatably mounted within the printing machine frame, and driven in the direction of arrow 14. Rotation of drum 10 causes photoconductive surface 12 to pass sequentially through a plurality of processing stations.

Initially, photoconductive surface 12 passes through charging station A which has positioned thereat a corona generating device, indicated at 16. Preferably, corona generating device 16 is arranged to extend substantially transversely across photoconductive surface 12. Upon being energized, corona generating device 16 charges surface 12 to a relatively high substantially uniform level. U.S. Pat. No. 2,836,725 issued to Vyverberg in 1958 describes a suitable corona generating device.

Drum 10 is, thereafter, rotated to exposure station B where a light-image of the original document is projected onto photoconductive surface 12 to selectively dissipate the charge thereon. The irradiated areas of photoconductive surface 12 are discharged to record thereon an electrostatic latent image corresponding to the original document. Exposure station B includes a stationary lens system, designated generally at 18, and a scan lamp 20. Original document 22 is positioned in a face down position upon reciprocating platen 24. Platen 24 is arranged to move in a generally horizontal plane as indicated by arrow 26. Scan lamp is disposed beneath transparent platen 24 to illuminate incremental portions of original document 22 moving thereover. The light reflected from original document 22 irradiates photoconductive surface 12, and selectively dissipates the charge thereon forming the electrostatic latent image.

After recording the electrostatic latent image on photoconductive surface 12, drum 10 rotates to development station C. At development station C, the electrostatic latent image recorded on photoconductive surface 12 is rendered viewable by the development apparatus of the present invention. This development apparatus will be described hereinafter in greater detail in conjunction with FIGS. 3 through 5, inclusive. In general, however, the development apparatus is adapted to cascade a developer mix over photoconductive surface 12 so that toner particles are electrostatically attracted to the latent image recorded thereon, thereby rendering the image visible.

A sheet of final support material 28 is advanced, in synchronism, with the powder image on surface 12 to transfer station D. At transfer station D, transfer corotron 30 electrostatically attracts the toner powder image from photoconductive surface 12 to support material 28, e.g. plain paper. A sheet transporting apparatus, designated generally at 32, advances support material 28 to transfer station D.

After transferring the powder image to support material 28, sheet transporting apparatus 32 advances support material 30 to fixing station E. Fixing station E includes a fuser 34 having suitable radiant heating ele ments and control circuits for maintaining the temperature thereof substantially constant to permanently affix the toner powder image to support material 28. Thereafter, sheet transporting apparatus 32 advances support material 28 to catch tray 36. When the support material is in catch tray 36, it may be readily removed therefrom by the machine operator.

Drum 10 nextpasses through cleaning station F, and, thereafter, discharge station G. At cleaning station F, a pre-clean corotron 38 applies a charge potential to photoconductive surface 12 which repels residual toner particles remaining thereon. Web cleaning system 40, then, removes the remaining toner particles therefrom. At discharge station G, light rays from scan lamp 20 are directed onto photoconductive surface 12 intermediate web cleaning system 40 and corona generating device 16. The light rays discharge any residual electrostatic charge remaining on photoconductive surface 12. The foregoing machine cycle is repeated for each copy.

FIGS. 2 through 4, inclusive, depict the development apparatus of the present invention. Turning now to FIGS. 2 and 3, the development apparatus indicated generally at 42, includes means for forming a flow of carrier granules. Carrier granules move from a storage region in the lower region of housing 44 to a discharge region in the upper region of development apparatus 42. Flow forming means or impeller 46 includes a hub member journaled for rotary movement in housing 44. I-Iub member 48 includes a plurality of equally spaced longitudinally extending vanes 52 mounted fixedly on the circumferential surface thereof. Drive means (not shown), such as a suitable motor, rotate impeller 46 in the direction of arrow at approximately 500 rpm. As impeller 46 rotates, it flings carrier granules S4 in an upwardly direction from the lower region of housing 44 to the discharge region which is positioned against intermingling means or guide member 56. Simultaneously therewith, toner particles 58 are dispensed into the discharge region. Toner particles 58 are stored in a hopper 70 formed by guide member 56 and side wall 60 of housing 44. Plate 62 is mounted slidably on side wall 60 and arranged to vary the size of the aperture defined by guide member 56 and side wall 60.

Referring now to FIG. 4, there is shown the detailed structural configuration of guide member 56. Guide member 56 has surface 64 thereof arranged to receive carrier granules 54 being flung thereat by impeller 46, and intermingle therewith toner particles 58 being discharged from hopper 70. Surface 64 is generally planar and has a plurality of transversely extending grooves 66 therein. Grooves 66 are positioned to extend transversely relative to one another so as to intermingle substantially homogenously carrier granules 54 with toner particles 58. In this way, toner particles 58 triboelectrically adhere to carrier granules 54 forming a substantially homogenous and uniform developer mix.

Turning now to FIG. 5, there is shown the detailed arrangement for discharging toner particles from hopper 70. The toner dispensing apparatus includes a shaft member 68 pivotably mounted in hopper 70. Shaft member 68 includes a plurality of spaced pin members 72 mounted substantially fixedly on the circumferential surface thereof. Pin members 72 extend outwardly from shaft member 68 substantially normal to the longitudinal axis thereof. Shaft member 68 is positioned in hopper 70 such that pin members 72 extend into the aperture in hopper 70 to control the amount of toner particles being dispensed therefrom. Lever arm 74 has one end portion thereof secured to one end portion of shaft member 68. Biasing means or spring member 76 pivots lever arm 74 into engagement with cam member 78. Suitable drive means (not shown), eg a motor, rotate cam member 78 in the direction of arrow 80. As cam member 78 rotates, it reciprocates lever arm 74 in the direction of arrow 82. This, in turn, reciprocates shaft member 68, in the direction of arrow 84, and oscillates pin members 72 in the aperture of hopper 70. in this manner, the rate of dispensing toner particles 58 is regulated. As shaft member 68 reciprocates, in the direction of arrow 84, toner particles 58 are dispensed from hopper 70. Toner particles 58 intermingle with carrier granules 54 in grooves 66 of planar surface 64 of guide member 56. The resultant homogenous mixture of toner particles 58 and carrier granules 54 moves in an upwardly direction transverse to photoconductor surface 12 and cascades thereover in a downwardly direction. As the developer mixture cascades over photoconductive surface 12, toner particles 58 are electrostatically attracted to the latent image. This produces a powder pattern on the latent image corresponding to the original document to be reproduced.

Thereafter, as hereinbefore described, the toner powder image is transferred from photoconductive surface 12 to support material 28. Support material 28 is, then, transported to fuser 34 where the toner powder image is permanently affixed thereto. Thereafter, support material 28 having the fixed image thereon is advanced to catch tray 36 where the operator removes the completed copy from the machine.

In recapitulation, it is apparent that the present invention produces a substantially homogenous mix of carrier granules and the toner particles for developing the electrostatic latent image recorded on the photoconductive surface. This is achieved, in the present invention, by a guide member adapted to intermingle the carrier particles with the toner particles. Furthermore, the quantity of toner particles being dispensed from the hopper is controlled by a simple device arranged to replenish toner particles utilized in the formation of powder images.

It is, therefore, evident that there has been provided in accordance with this invention, a development apparatus that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. An electrophotographic printing machine of the type having a corona generating device for charging a photoconductive surface to a substantially uniform level, and an exposure mechanism for irradiating the photoconductive surface with a light-image to record thereon an electrostatic latent image of an original document to be reproduced, wherein the improvement includes:

means for forming a flow of carrier granules moving from a storage region to a discharge region;

a hopper having an aperture therein in the lower region thereof, said hopper storing a quantity of toner particles arranged to be dispensed through the aperture therein into the discharge region;

a shaft member mounted pivotably in said hopper;

a plurality of spaced pin members mounted substantially fixedly on the circumferential surface of said shaft member and extending outwardly therefrom substantially normal to the longitudinal axis thereof, said shaft member being positioned such that said pin members are disposed substantially in the aperture of said hopper;

means for reciprocating said shaft member about the longitudinal axis thereof so that said pin members feed toner particles toward the aperture of said hopper; and

means for intermingling carrier granules with toner particles producing a substantially uniform mix, and, substantially simultaneously therewith, directing the flow of mix to cascade over the photoconductive surface creating a toner powder image on the electrostatic latent image recorded thereon.

2. An electrophotographic printing machine as recited in claim 1, wherein said flow forming means includes:

a hub member journaled for rotary movement;

drive means for rotating said hub member; and

a plurality of substantially equally spaced longitudinally extending vanes mounted fixedly on the circumferential surface of said hub member.

3. An electrophotographic printing machine as recited in claim 1, wherein said reciprocating means includes:

a lever arm having one end portion thereof secured to said shaft member;

a cam member journaled for rotary movement; and

biasing means for urging resiliently the other end portion of said lever arm into engagement with said cam member, said cam member being adapted to reciprocate said shaft member about the longitudinal axis thereof.

4. An electrophotographic printing machine as recited in claim 1, wherein said intermingling and directing means includes a guide member having a generally planar surface with a plurality of grooves extending substantially transversely to one another, said guide member being positioned in the discharge region with the generally planar surface thereof arranged to receive carrier granules in the grooves therein for mixing substantially uniformly toner particles therewith. 

1. An electrophotographic printing machine of the type having a corona generating device for charging a photoconductive surface to a substantially uniform level, and an exposure mechanism for irradiating the photoconductive surface with a light-image to record thereon an electrostatic latent image of an original document to be reproduced, wherein the improvement includes: means for forming a flow of carrier granules moving from a storage region to a discharge region; a hopper having an aperture therein in the lower region thereof, said hopper storing a quantity of toner particles arranged to be dispensed through the aperture therein into the discharge region; a shaft member mounted pivotably in said hopper; a plurality of spaced pin members mounted substantially fixedly on the circumferential surface of said shaft member and extending outwardly therefrom substantially normal to the longitudinal axis thereof, said shaft member being positioned such that said pin members are disposed substantially in the aperture of said hopper; means for reciprocating said shaft member about the longitudinal axis thereof so that said pin members feed toner particles toward the aperture of said hopper; and means for intermingling carrier granules with toner particles producing a substantially uniform mix, and, substantially simultaneously therewith, directing the flow of mix to cascade over the photoconductive surface creating a toner powder image on the electrostatic latent image recorded thereon.
 2. An electrophotographic printing machine as recited in claim 1, wherein said flow forming means includes: a hub member journaled for rotary movement; drive means for rotating said hub member; and a plurality of substantially equally spaced longitudinally extending vanes mounted fixedly oN the circumferential surface of said hub member.
 3. An electrophotographic printing machine as recited in claim 1, wherein said reciprocating means includes: a lever arm having one end portion thereof secured to said shaft member; a cam member journaled for rotary movement; and biasing means for urging resiliently the other end portion of said lever arm into engagement with said cam member, said cam member being adapted to reciprocate said shaft member about the longitudinal axis thereof.
 4. An electrophotographic printing machine as recited in claim 1, wherein said intermingling and directing means includes a guide member having a generally planar surface with a plurality of grooves extending substantially transversely to one another, said guide member being positioned in the discharge region with the generally planar surface thereof arranged to receive carrier granules in the grooves therein for mixing substantially uniformly toner particles therewith. 